Convert CONFIG_SPL_BOARD_INIT to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_BOARD_INIT

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
[trini: Update the Kconfig logic]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/README b/README
index 864bf8b..350b805 100644
--- a/README
+++ b/README
@@ -292,7 +292,7 @@
 	- stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined and
 		CONFIG_SPL_STACK_R_ADDR points into SDRAM
 	- preloader_console_init() can be called here - typically this is
-		done by defining CONFIG_SPL_BOARD_INIT and then supplying a
+		done by selecting CONFIG_SPL_BOARD_INIT and then supplying a
 		spl_board_init() function containing this call
 	- loads U-Boot or (in falcon mode) Linux